Rock Pooling: August 2015

The intertidal sediments experience periods of erosion and deposition which in turn influence the organisms found on the shore.

Strong winds and waves resulted in the erosion of the finer sediments to reveal a pebble bed below, but what was astonishing was that barnacles and polychaete worm tubes were among the cobbles, even though the substrate had not long been exposed.....

Erosion of the finer sediments, have left coarser sediments exposed. Habitat classification: LS.Sa (Littoral sand) EUNIS A2.2 and LS.LCS (Littoral coarse sediments) A2.1

Polychaete worm tubes occur amongst the coarser sediments of the lower shore.

The occurrence of the polychaete worm tubes is quite extensive.

There are even barnacles on the cobbles!

This is quite intriguing as the shore is so variable and the coarser sediments are often covered as shown below.

The shore in December, 2014.

The shore in Summer, 2014

The shore in September, 2012

Steep cliffs surround the bay, the lower craggy edges covered in lichens. The cliff bases and steeper bedrock transition between the lichen and barnacle communities with limpets, periwinkles and whelks. Boulders and bedrock on the shore host a similar barnacle community plus a variety of seaweeds, including where sand scour is event, ephemeral seaweeds. Rockpools occur throughout the shore, and a river flows downs from the cliffs.

The bay experiences a dynamic regime, alternating between periods of erosion (stony) and deposition (sandy).The underlying substrate is boulders and bedrock, however, variable amounts of sand may be deposited on top, sourced from the sand bar situated offshore. The communities encountered reflect the alternation between these regimes.

For the past 18 months the shore has been stony and a series of rockpooling visits has documented the slow colonisation and succession of the sea shore communities of the newly available substrate.

Please see previous blog posts:
http://thesaltyscavenger.blogspot.nl/2015/07/rockpooling-destination-revisit-lands.html
http://thesaltyscavenger.blogspot.nl/2014/05/revisit-lands-end-peninsular-april-2014.html
http://thesaltyscavenger.blogspot.nl/2014/02/rockpooling-destination-lands-end.html

Habitat classification:

Substrate	LR (Littoral rock)						LS (Littoral Sediments)
Habitat	LR.HLR (High energy littoral rock)	LR.MLR (Moderate energy littoral rock)	LR.FLR (Features of littoral rock)				LS.Lsa (Littoral Sand)
Biotope complex	LR.HLR.MusB (Mussel and/or barnacle communities)	LR.MLR.BF (Barnacles and fucoids on moderately exposed shores)	LR.FLR.Rkp (Rockpools)		LR.FLR.Eph (Ephemeral green or red seaweed communities)	LR.FLR.Lic (Lichens and small green algae on suprallitoral and littoral fringe rock)	LS.LSa.St (Strandline)
Biotope		LR.MLR.BF.Fser.R (Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock)	LR.FLR.Rkp.Cor (Coralline crust dominated shallow eulittoral rockpools)	LR.FLR.Rkp.SwSed (Seaweeds in sediment-floored eulittoral rockpools)

Below are images of organisms you may encounter whilst rockpooling in these habitats:

The rocky shore during the current visit in June 2015, shows little variation from April 2015. The only noticeable difference is an increased 'bleaching' of ephemeral green seaweed by the stack.

The rocky shore in April 2015

A stream flows over the cliff, onto the shore and beneath the cobbles and boulders.

Rough periwinkles (Littorina spp) occur on the littoral fringe and upper shore bedrock of the stack.

Small periwinkles (Melarhaphe neritoides) seek refuge within the pits of the larger boulders.

Small periwinkles (Melarhaphe neritoides) seek refuge within a pit of a large boulder.

Rough and small periwinkles (Littorina spp and Melarhaphe neritoides) aggregate within crevices of a large boulder.

The first barnacles are beginning to appear on the boulders that were once covered by sand.

Sparse barnacles on boulders that were once covered by sand.

Since April 2015, a strandline of seaweed has formed on the shore and much seaweed has collected within the cave. Habitat classification: LS.LSa.St (Strandline) EUNIS: A2.21.

Seaweed has been washed up among the boulders of the upper shore.

This photograph taken in April 2015, shows no strandline on the upper shore or, within the cave. The presence of the strandline suggests that the shore has experienced storms or, strong tides during the intermittent rockpooling periods which have washed seaweed up on to the shore.

Ephemeral green seaweed covers boulders and rock surrounding the stack. Compared to April, the seaweed shows signs of 'bleaching'. Habitat classification: Habitat classification: LR.FLR.Eph (Ephemeral green or red seaweed communities) EUNIS: A1.45.

The habitats of the shore are influenced by wave exposure, sand scour, fresh water run off and desiccation. The result is a patchwork of biotopes that are not distributed evenly down the shore. In general boulder tops are covered by fucoids and/or barnacles, whilst ephemeral green seaweed lace the river diluted rockpools and lastly sand scour tolerant seaweeds occur in scoured rockpools and on the lower shore. Habitat classification: LR.MLR.BF (Barnacles and fucoids on moderately exposed shores) EUNIS: A1.21, LR.FLR.Eph (Ephemeral green or, red seaweeds (Fresh water or sand influenced) EUNIS: A1.45 and LR.FLR.Rkp (Rockpools) EUNIS: A1.41.

Fucoids cover the boulders, whist ephemeral green seaweed lace the diluted and sand scoured rockpools. Is this prolific seaweed growth due to the recent availability of substrate? Grazers occur at low abundance on the upper shore, much more so than in comparison to the cliff edges and barnacle cover is less, resulting in reduced competition for space and grazing pressures, enabling seaweeds to takeover.

Fucoids cover the boulders, whilst ephemeral green seaweed covers the sand scoured bedrock.

Grazers occur at low abundance among the boulders of the upper shore. Limpets are the most obvious motile species where they occur at low abundances, largely confined to boulder crevices.

In areas of the shore that are rarely covered by sand the extent of fucoid cover depends largely on wave exposure, with the cliff bases and the wave exposed boulders supporting fewer fucoids. In these habitats seaweeds are largely confined to the lower bedrock beneath.

The barnacle communities support beadlet anemones (Actina equina), Limpets (Patella spp) and ephemeral green seaweeds.

The seaweed communities below on the lower shore are comprised of fucoids, robust red seaweeds and sand tolerant seaweeds. Habitat classification: LR.MLR.BF.Fser.R (Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock) EUNIS: A1.2141.

Fucus serratus and red seaweeds including, Rhodothamniella floridula and Mastrocarpus stellatus.

Fucus serratus and Mastrocarpus stellatus.

Fucus serratus, Mastrocarpus stellatus and Himanthalia elongata.

Flat periwinkles (Littorina spp) on Fucus serratus.

Flat periwinkles (Littorina spp)

Mastrocarpus stellatus

Rhodothamniella floridula

Flat periwinkle (Littorina spp)

In the rockpools of the lower shore there is an explosion of seaweeds.

The rockpools support a variety of species, including may sand tolerant seaweeds.
Habitat classification: LR.FLR.Rkp.SwSed (Seaweeds in sediment-floored eulittoral rockpools) EUNIS: A1.413.